On Mar. 22, 1975, a fire at the Browns Ferry Nuclear Power Plant fundamentally changed the concept of fire protection and associated regulatory requirements for U.S. nuclear power plants. Plant workers were fixing leaks in the cable spreading room outside the reactor building. The workers used a candle to test seals for air leaks into the reactor building. The polyurethane foam seal, however, was not fire-rated. The flame from the candle ignited both the seal and the electrical cables that passed through it.
By the time the fire was extinguished, it had burned for almost 7 hours. More than 1600 electrical cables were affected, 628 of which were important to plant safety. The fire damaged electrical power, control systems, and instrumentation cables and impaired cooling systems for the reactor. Operators could not monitor the plant normally and had to perform emergency repairs on systems needed to shut the reactor down safely.
Investigations after the fire revealed deficiencies in the design of fire protection features at nuclear power plants and in the plant procedures for responding to a fire. Fire insurance companies, normally concerned with occupant safety and property protection, did not sufficiently consider nuclear safety issues. A fire in certain locations at a nuclear plant could cause redundant safety systems and components to fail, making it difficult to shut the reactor down safely.
After the Browns Ferry fire, the Nuclear Regulatory Commission (NRC) revised its fire protection regulations to reduce the chances of a fire starting and the consequences should a fire occur. Under these regulations, each licensee is required to maintain the ability to shut down the reactor safely in the event of a fire. More specifically, the objectives of the regulations are to: (1) minimize the potential for fires and explosions, (2) rapidly detect, control, and extinguish fires that do occur; and (3) ensure that fire will not prevent operators from shutting down the reactor safely or increase the risk of significant radioactive releases to the environment.
Nuclear power plants have begun to implement redundant methods of fire protection to keep fires from damaging plant safety systems. Some of these methods include fire barriers, fire detection systems, and fire suppression systems (such as sprinklers). If a required element of fire protection is not available, the licensee must compensate for it using ‘Compensatory Measures,’ which often include placing dedicated personnel on a fire watch. The NRC regularly inspects licensees' means of achieving and maintaining the safe shutdown of their reactors in the event of a fire.
In addition, plant workers are required to obtain permits before performing work that could potentially affect the fire safety posture of a plant or fire area. These permits must be obtained before work is performed on barriers such as walls or doors, suppression systems such as sprinkler systems, detection systems such as smoke detectors, ‘Hot Work’ such as welding or the use of flame-based heaters, and the movement of Transient Combustibles such as fuel, paint or large amounts of flammable clothing.
Existing techniques for complying with NRC fire protection requirements have a number of drawbacks. Perhaps most importantly, these techniques are mostly manually performed and paper-based. For example, work permits are created on paper and tracked in filing cabinets. Compensatory measures are calculated by hand, which proves to be tedious and prone to error.
Some efforts have been made to improve fire risk management in nuclear power plants. These efforts involve the use of a database to track work permits. However, these databases are passive in nature, serving merely to store and output data. They are not equipped, for example, to perform rules-based decision-making, probabilistic risk assessments, compensatory measures calculations, or any other type of complex processing. Thus, even with these databases, the need for human intervention to review and approve the substance of the permits in view of prevailing NRC safety rules is significant.
A need therefore exists for a system and method of providing information for managing risk in a power plant in a way that will ensure compliance with NRC and/or other fire safety requirements, which system and method may automatically be performed by a integrated rules-based processing engine that requires virtually no human intervention, that significantly reduces the time, cost, and efficiency of managing the plant, and which provides a more reliable safeguard against fire hazards.